A. I. Stadnichenko

The Thermal Stability of Nanodiamond Surface Groups and Onset of Nanodiamond Graphitization

Abstract The results of study of the surface chemistry of nanodiamonds treated by a mixture of HClO4 and H2SO2 acids are presented. Changes of the composition of surface diamond groups brought up by thermal annealing were monitored by Fourier transformed infrared spectroscopy and temperature‐programmed desorption. The decomposition of oxygen‐containing groups is observed at 300–900°C; CHx groups decompose at 700–1150°C. The process of the annealing of ND was investigated by the X‐ray photoelectron spectroscopy. The clear onset of ND graphitization was observed at temperature of 950°C that is supported by the appearance of sp 2 component in the C1s spectrum. The presence of the N1s peak in spectra of ND is observed in initial and partially graphitized ND annealed up to 1100°C.

Oxidation of the polycrystalline gold foil surface and XPS study of oxygen states in oxide layers

Gold oxide films obtained on the surface of polycrystalline gold foil upon oxidation by oxygen activated by a high-frequency discharge have been studied by X-ray photoelectron spectroscopy. High-frequency O2 activation affords oxide films more than 3–5 nm thick. As follows from Au4f spectra, the surface gold atoms are oxidized to the oxidation state +3. The O1s spectra have a composite shape and are decomposed into four components that characterize nonequivalent states of oxygen in the resulting oxide films. It is assumed that the two major oxygen states (Eb(O1s) = 529.0 and 530.0 eV) correspond to the oxygen atoms in two-and three-dimensional gold oxide Au2O3, respectively. The oxygen states characterized by the higher binding energies (Eb(O1s) = 531.8 and 535.2 eV) likely correspond to molecular oxygen in peroxide and superoxide groups, respectively.

Highly Oxidized Platinum Nanoparticles Prepared through Radio‐Frequency Sputtering: Thermal Stability and Reaction Probability towards CO

Platinum-oxide nanoparticles were prepared through the radio-frequency (RF) discharge sputtering of a Pt electrode in an oxygen atmosphere. The structure, particles size, electronic properties, and surface composition of the RF-sputtered particles were studied by using transmission electron microscopy and X-ray photoelectron spectroscopy. The application of the RF discharge method resulted in the formation of highly oxidized Pt(4+) species that were stable under ultrahigh vacuum conditions up to 100 °C, indicating the capability of Pt(4+) -O species to play an important role in the oxidation catalysis under real conditions. The thermal stability and reaction probability of Pt(4+) oxide species were analyzed and compared with those of Pt(2+) species. The reaction probability of PtO2 nanoparticles at 90 °C was found to be about ten times higher than that of PtO-like structures.

Copper-cerium oxide catalysts for the selective oxidation of carbon monoxide in hydrogen-containing mixtures: I. Catalytic activity

A series of copper-cerium oxide catalysts were prepared, and their properties toward the reaction of CO oxidation in hydrogen-containing gas mixtures were studied. It was found that the copper-cerium oxide catalysts are stable, active, and selective in this reaction. The conditions under which these catalysts decreased the concentration of CO from 1 to <10−3 vol % in hydrogen containing water vapor and carbon dioxide were determined.

Reactivity and thermal stability of oxidized copper clusters on the tantalum(V) oxide surface

Oxidized copper clusters 2–5 nm in size have been obtained by RF discharge sputtering of a copper wire in an oxygen atmosphere. Isolated CuO clusters or, at long deposition times, their agglomerates form on the support. The thermal stability of the oxidized nanoparticles in a vacuum and their reactivity toward CO in relation to the deposition time have been investigated by X-ray photoelectron spectroscopy. The asprepared clusters show low reactivity (10−7−10−9), but their activation by reduction and subsequent reoxidation in an oxygen medium raises their reactivity to ∼10−5. This is due to the appearance of weakly charged oxygen species on the surface. The reactivity of the CuO clusters has been compared to the reactivity of earlier studied nanosized copper oxide model objects.

An active phase transformation on surface of Ni-Au/Al2O3 catalyst during partial oxidation of methane to synthesis gas

It was studied the influence of gold addition on physico-chemical properties and catalytic activity of bimetallic Ni-Au/Al2O3 catalyst in partial oxidation of methane (POM). The reduction behavior in hydrogen, XRD crystal structure, XPS spectra and POM catalytic activity were investigated. The reduction of Ni-Au catalyst is a prerequisite condition to catalyze POM reaction. The formation of Ni-Au alloy during high temperature reduction in hydrogen and also in the conditions of POM reaction was experimentally proved. The addition of gold to Ni/Al2O3 system improves catalyst stability and activity in POM reaction.

Copper-cerium oxide catalysts for the selective oxidation of carbon monoxide in hydrogen-containing mixtures: II. Physicochemical characterization of the catalysts

The copper-cerium oxide catalysts were characterized using a set of physicochemical techniques including in situ FTIR spectroscopy, XPS, and XRD. It was found that copper segregated on the surface of cerium oxide and its states were labile and dependent on catalyst pretreatment conditions. Copper in a dispersed state was responsible for the reaction of CO oxidation in the presence of H2 on the copper-cerium oxide catalysts. It is likely that this state of copper was composed of two-dimensional or three-dimensional surface clusters containing Cu+ ions.

Synthesis and physicochemical characterization of palladium-cerium oxide catalysts for the low-temperature oxidation of carbon monoxide

The effect of CeO2 preparation procedure on the electronic and structural states of the active component of Pd/CeO2 catalysts and their activity in the low-temperature reaction of CO oxidation was studied. The following two nonequivalent states of palladium were detected in the catalysts having low-temperature activity using XPS and IR spectroscopy: Pd0(Pdδ+) as the constituent of a palladium-reduced interaction phase and Pd2+ as the constituent of a palladium-oxidized interaction phase PdxCeO2 −δ. It was found that the procedure used for preparing a CeO2 support considerably affected the formation of these phases and quantitative ratios between them. It was demonstrated that the palladium-oxidized interaction phase was responsible for low-temperature activity, whereas the palladium-reduced interaction phase was responsible for activity in the region of medium and high temperatures.

Constitution and Properties of Nanocomposites Prepared by Thermal Decomposition of Silver Salts Sorbed by Polyacrylate Matrix

Constitution and dispersity of the products of thermal decomposition of silver nitrate ammonia complex sorbed by polyacrylate matrix are studied by the methods of small- and wide-angle X-ray scattering, optical, photoelectron and Auger-electron spectroscopies. It is shown that, at temperatures of 140–150°C, the complete decomposition of the complex occurs with the formation of nanoparticles and charged silver clusters in polymer bulk. No initial or intermediate products were observed. The average size of obtained nanoparticles is equal to 5 nm. The particles with the size less than 5 nm are amorphous according to X-ray data. The stabilization of nanoparticles occurs due to the adsorption of acrylic copolymer (presumably, via oxygen atoms) on their surfaces. Upon long-term storage in air, the self-diffusion of silver particles and clusters takes place from the surface to composite bulk caused by the detachment of oxygen-containing groups occurring at the metal–polymer interface.

Transformation of a Pt-CeO2 Mechanical Mixture of Pulsed-Laser-Ablated Nanoparticles to a Highly Active Catalyst for Carbon Monoxide Oxidation

The pulsed laser ablation (PLA) in alcohol and water media was employed to prepare Pt and CeO2 PLA‐nanoparticles of different sizes and degrees of defectiveness. Interactions of metallic platinum and ceria particles were studied using the thermal activation of Pt–CeO2 mechanical mixtures in the CO+O2 reaction medium or O2 atmosphere. The thermal activation resulted in oxidized Pt2+/Pt4+ states of platinum in the surface solid solutions PtCeOx and/or PtOx clusters. Catalysts formed after calcination of the PLA‐ablated Pt–CeO2 mixtures in oxygen at 450–600 °C revealed CO conversion at very low temperatures up to 70 % depending on the conditions of PLA particles preparation and thermal activation of Pt–CeO2 mechanical mixture.